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What is safe/safer?

Does 20mph make roads safer? Eric Bridgstock Independent Road Safety Researcher St Albans National Road Safety Conference 13 November 2013. What is safe/safer? . Safe = free from harm or exposed to an acceptable level of risk Safer = less risk Success measured by reduced casualties

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What is safe/safer?

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  1. Does 20mph make roads safer?Eric BridgstockIndependent Road Safety ResearcherSt AlbansNational Road Safety Conference13 November 2013

  2. What is safe/safer? Safe = free from harm or exposed to an acceptable level of risk Safer = less risk Success measured by reduced casualties Casualties result from accidents So what causes “accidents”?

  3. The Recipe for an Accident A collision/accident needs hazard or hazardous condition AND triggering event This combination initiates an accident sequence, which will become a collision unless something can prevent it …

  4. Hazards and Events • Hazards - driver or vehicle • Other hazards - weather conditions, road layout, other road users • Triggering events - misjudgement, poor observation, lapse of concentration, unsignalled manoeuvre, act of aggressive driving, vehicle failure, falling asleep • A collision can be prevented by • removing or mitigating the hazard • preventing the triggering event • mitigating the consequences (accident sequence)

  5. Accident Sequence Hazard Triggering Event

  6. Could a 20mph limit prevent a collision? • Speed limits encourage lawful drivers to drive at, or below, the prevailing speed limit • Is a lawful driver exceeding a speed limit a hazard? If they were, then lowering a speed limit would immediately make vehicles “hazardous” that were previously not hazardous – that is obviously illogical, since the number on a sign has negligible bearing on an accident scenario • Any moving vehicle is hazardous to some degree, and that hazard may vary with speed but there is no speed threshold that would be recognised as intolerable • 20mph does not remove hazards (or have any measurable positive effect on them)

  7. Could a 20mph limit remove triggering events? No! But 20mph limit create hazards and triggering events: • Pedestrians encouraged to feel safer, so take less care when walking into the road • Slow speeds can also reduce driver concentration levels 20mph does not make roads safer it actually makes them LESS SAFE • 20mph cannot mitigate or terminate an accident sequence - that involves driver skill, crash barriers, seatbelts, air-bags, crumple zones, ABS, etc. and even luck!

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